This study uses the spontaneously hypertensive rat (SHR), a genetically hypertensive animal which is compared with a normotensive strain (WKY). The overall goal is to understand why the hypertensive rats have more active sympathetic nervous system function. In the past year careful quantitative measurements were made of how effective the baroreceptor reflex mechanisms are in the hypertensive animals. These reflex mechanisms tend to hold blood pressure down by cutting back on sympathetic nerve activity and a deficiency might explain the greater activity in the hypertensive animals. The results showed that, to the contrary, the hypertensive animals have a very potent reflex capability. Hence, the increase sympathetic activity must be due to an inherent hyperexcitability within the nervous system. Additional observations suggest that some of the increased activity may be due to differences within the peripheral sympathetic ganglia and experiments will be carried out in the coming year to test this concept. These studies intend to provide basic information about the way in which the brain, and its reactions to stress, are involved in the appearance of high blood pressure in some individuals.